When you need .docx instead of .odt
Many people, offices and portals work only with Microsoft Word files. If your document was written in LibreOffice or OpenOffice — or someone sent you an .odt file — converting it to .docx makes it easy to edit in Word, Google Docs or WPS and to submit where Word files are required.
What happens when you convert
The ODT is unpacked in your browser, and its headings, paragraphs, lists, tables and embedded pictures are rebuilt as a new .docx document. The result is fully editable in Word.
What is simplified
Advanced features — page styles, headers and footers, footnotes, text frames, columns, comments, tracked changes and fields such as automatic tables of contents — are not converted. Fonts may be replaced by Word's defaults. For complex documents, LibreOffice's own File → Save As → Word format gives the most complete result.
Common problems and how to fix them
Headers and page numbers are missing: add them again in Word with Insert → Header and Page Number. A table looks different: adjust column widths in Word. A picture is missing: it was linked rather than embedded in the ODT.
Good habits
Check the document in Word before sending, keep the original ODT, and use ODT to PDF when the receiver only needs to read the document.